1. Field of the Invention
The invention relates to a corrosion resistant article having a sulfide coating of a refractory metal formed thereon, and to a method for making this article.
2. Description of the Prior Art
In various applications, and particularly in deep, gas and oil-well production and drilling applications, there is a need for material that is corrosion resistant, and particularly resistant to corrosion caused by sulfide environments, such as those containing hydrogen sulfide. In deep-well production and drilling applications, commonly termed sour well applications, the drilling components, and particularly the tubing extending into the well, are subject to environments containing various levels of hydrogen sulfide often in combination with carbon dioxide, brine and various hydrocarbons. Tubing used for this purpose is for reasons of economy made from carbon steel. In the presence of hydrogen sulfide encountered in sour well applications, corrosion of the carbon steel occurs as a result of the iron reacting to form iron-sulfide phases, particularly on the inner wall surfaces of the tubing extending into the well and subjected to the sulfide environment.
More particularly, in sour gas environments, the iron-containing alloy, e.g. carbon steel, undergoes attack by sulfur-containing compounds such as hydrogen sulfide, resulting in the formation of a scale of various ferrous sulfide phases such as pyrite and marcasite (FeS.sub.2); pyrrhotite (Fe.sub.1-x S) and mackinawite (Fe.sub.1+x S). In accordance with the present invention, it has been found that ferrous ions are rapidly transported through such sulfide phases, in particular the pyrrhotite phase, and react with the sulfur-containing compound at the outer surface leading to the corrosion process. It has been found that the iron ion is rapidly transferred through the iron sulfide formation, which is typically in the form of sulfide scale. The propogation or transport of the iron ion through the iron sulfided steel is relatively rapid and thus the corrosion is severe upon exposure of carbon steel tubing to hydrogen sufide environments.